1. Field of the Invention
The present invention relates to a semiconductor device which has a circuit including a thin film transistor (hereinafter referred to as a TFT) and a method for manufacturing the semiconductor device.
Note that the term “semiconductor device” in this specification refers to devices in general that can operate by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic devices are all included in the semiconductor device. Examples thereof include electro-optical devices typified by display devices using liquid crystal and the like, and electronic devices incorporating these electro-optical devices as components.
2. Description of the Related Art
Display devices are widely spread as liquid crystal display televisions, displays for personal computers, cellular phones, and the like, in many of which liquid crystal display devices that include as switching elements thin film transistors using amorphous silicon (hereinafter referred to as amorphous silicon TFTs) are used.
One type of liquid crystal display devices that include amorphous silicon TFTs as switching elements is a fringe field switching (FFS) mode LCD. The FFS mode is a technique for improving aperture ratio and transmittance of in-plane switching (IPS) mode LCDs, details of which are described in Reference 1 (Reference 1: Japanese Published Patent Application No. 2001-235763).
In a conventional amorphous silicon TFT, its stacked structure is formed using six masks by a photolithography step. However, reduction in the number of steps has been desired in order to reduce manufacturing cost or to increase yield.